Detecting ammonia in measurement gas (such as exhaust gas from an internal combustion engine) using an ammonia sensor is a known art.
An ammonia detection signal that varies according to the result of detection by the ammonia sensor is outputted from, for example, a sensor controller that controls the ammonia sensor. The ammonia detection signal is used, for example, by an internal combustion engine controller to control the internal combustion engine. The internal combustion engine control system is configured to include the internal combustion engine controller, the ammonia sensor, and the sensor controller.
Some ammonia sensors react not only to ammonia but also to another specific gas (such as a flammable gas). An ammonia detection signal obtained using such an ammonia sensor varies not only due to the influence of ammonia but also due to the influence of the specific gas, and therefore the accuracy of detection of ammonia may decrease.
A technique proposed to address this issue is to detect the concentration of oxygen in the exhaust gas and then correct, on the basis of the oxygen concentration detected, the result of detection of ammonia that is obtained through the ammonia detection signal (Japanese Patent Application Laid-Open (kokai) No. 2016-065862). With this technique, the reduction in the accuracy of detection of ammonia due to the influence of the specific gas can be suppressed.